The invention relates to a device for determining the mass of a motor vehicle utilizing signals from: signal transmitters for the engine torque, signal transmitters for the speed and acceleration of the vehicle, signal transmitters for the state of a clutch between the engine and drive train and wherein a computer evaluates the signals from these signal transmitters. The device determines a coefficient for the running resistance of the vehicle during a first operating phase with the clutch disengaged. The device repeatedly determines values for the acceleration of the vehicle during a second operating phase with the clutch engaged. A value correlated with the mass of the vehicle is calculated repeatedly by forming the quotient of the engine torque, determined during the second operating phase, and a quantity dependent on the difference between the acceleration value and the running resistance.
A corresponding device is the subject of European Patent Specification 0,111,636. This publication makes use of the knowledge that the mass of a motor vehicle can be determined (with its rotating masses being ignored) by forming a difference quotient between two values of the drive torque determined at different moments and the difference between two values of the vehicle acceleration determined at corresponding moments. The calculation can be simplified, with the accuracy being enhanced at the same time, if one moment is located in an operating phase with a vanishing drive torque, that is to say an operating phase in which the clutch connecting the engine to the drive train is disengaged (see lines 9 to 12 on page 3 of European Patent Specification 0,111,636). The attainable accuracy is nevertheless still not fully satisfactory.
The object of the instant invention is to provide a device of a similar character which makes it possible to enhance the accuracy of the determination of the mass substantially.
According to the invention, this object is achieved by virtue of the fact that a signal transmitter reproducing the particular transmission ratio is provided and the mass is determined by means of a computer, according to: ##EQU1## in which b.sub.ei =acceleration values of the vehicle with the clutch engaged
.eta.=the efficiency of the drive train PA1 i.sub.G =ratio of the transmission PA1 r=dynamic rolling radius of the drive wheels PA1 J.sub.M =moment of inertia of the engine PA1 M.sub.Mi =values of the drive torques and engine torques
The invention takes into consideration the fact that the moment of inertia of the vehicle engine represents a considerable quantity and should therefore be taken into account in the calculation of the vehicle mass.
Moreover, the invention makes it possible to achieve an enhanced accuracy because the coefficient of running resistance is evaluated very precisely and the signals representing the engine torque and acceleration are evaluated repeatedly during an engine operating phase with the clutch engaged.
According to a preferred embodiment of the invention, there is also a brake-signal transmitter which makes it possible to ensure that signals of the signal transmitters, which are generated when the brake is being actuated, are ignored, that is to say only those signals generated when the vehicle brake is not being actuated are used to determine the vehicle mass.
The values of the vehicle acceleration can be determined from the running speed by determining the difference quotient from the difference between two speed values measured at different moments and the time interval of these two measurements.
Since the acceleration of the vehicle always fluctuates about an average value, it is expedient if a multiplicity of measurements is carried out during a predetermined time period and an average value of these measurements formed. This can prevent the possibility that vibrations in the drive train, or comparatively high-frequency fluctuations of the values of the vehicle speed and acceleration, will result in a falsification of the value of the mass determined.
As a signal transmitter for the particular transmission ratio, revolution transmitters can be provided on the input side and output side of the transmission and the computer can calculate from their output, the quotient of the rates of revolutions on the input and output sides and consequently the transmission ratio.
In order to determine the drive torque, there can be a signal transmitter, the signals of which represent the particular position of the injection pump on a diesel engine, or of the throttle flap in a gasoline engine.
If characteristic engine data of the particular injection-pump or throttle-flap position and the related revolution of the engine are stored in the computer, the latter can determine the drive torque or engine torque directly.
It is advantageous if there is a brake-signal transmitter provided to indicate if vehicle brakes are applied and that signals from the remaining signal transmitters, generated when the brake is being actuated, are ignored.
It is also advantageous if the acceleration signals are determined through successive speed measurements and times with the values being averaged.
The ratio of the transmission is obtained through revolution transmitters arranged on the input and output side of the transmission.
The computer can assign a value for the particular engine torque (M.sub.Mi) in response to a signal transmitter representing the position of the accelerator pedal, or the operating state of the injection pump of the engine, when engine data is stored in the computer. The computer additionally takes into account the rate of revolutions of the engine.
It is advantageous if the signals representing the acceleration (b.sub.a, b.sub.ei) are utilized only below a limiting speed. This will reduce the influence of the air resistance of the vehicle.